Oxygen-scavenging containers having low haze

ABSTRACT

A container providing effective oxygen-scavenging functionality, while having low haze. The container has at least one wall, wherein the wall comprises a populated area, and wherein the populated area comprises a film-forming polymer; and a population of particles comprising an effective amount of oxygen-scavenging particles, wherein the number of particles of said population does not exceed a concentration of about 
         (6×10 7  particles÷T) per cubic centimeter of polymer wherein T is the thickness of the populated area in mils; and wherein the wall has a transmission Hunter haze of up to about 1 percent per mil of the container wall.

CROSS-REFERENCE

This application is a continuation of pending application Ser. No.10/195,385 filed Jul. 16, 2002 which is a continuation in part of Ser.No. 09/916,671, filed on Jul. 26, 2001 which is now U.S. Pat. No.6,780,916 all of which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Thermoplastic resins such as polyethylene terephthalate (PET) arecommonly used to manufacture packaging materials. PET processed underthe right conditions produces high strength articles with excellent gasbarrier properties. Foods, beverages, and medicines can deteriorate orspoil if exposed to oxygen. To improve shelf life and flavor retentionof products such as foods, beverages, and medicines, therefore, thebarrier protection provided by PET is often supplemented with additionallayers of packaging material or with the addition of oxygen scavengers.

Adding a layer of gas barrier film is known as passive-barrierpackaging. Ethylvinyl alcohol (EVOH), Polyvinylidene dichloride (PVDC),and Nylon MXD6, are examples of films commonly used for this purpose dueto their excellent oxygen barrier properties. Using distinct layers ofdiffering materials is not preferred, however, because it adds cost topackaging construction and does not reduce the levels of oxygen alreadypresent in the package.

Adding oxygen scavengers to the PET resin is known as active-barrierpackaging. This approach to protecting oxygen-sensitive products istwo-fold; the packaging prevents oxygen from reaching the product fromthe outside, and also absorbs some of the oxygen present in thecontainer and from within the polymer matrix. In some applications,small packets or sachets containing oxygen scavengers are added to thepackaging container and lie next to the food. Sachets are generallylimited to solid foods, where the sachet can be readily removed from thefoodstuff and not accidentally ingested. Construction of the sachets andthe cumbersome nature of their introduction into the package result inincreased costs.

One way to overcome the disadvantages of sachets is to incorporate thescavenger directly into the wall of the food package. This can be doneby placing the scavenger throughout the scavenger wall or placing thescavenger in a unique layer between many layers of the containersidewall. It should be appreciated that references to the sidewall andwall include the lid and bottom sides of the container. At present theincorporation of the scavenger throughout the container wall is found innon-transparent trays or packaging films where the scavenger is notvisible. Virtually any scavenger can be used in this application becausethe scavenger is not visible. However, containers requiring clarity haveheretofore been limited to organic type scavengers that maintain theirclarity when placed in a separate layer in the wall of the container.The use of the organic scavenger in a mono-layer or single-layerconstruction is limited by cost and regulatory constraints due to thenature of the organic scavenger or the by-products of the scavengingreaction.

Contributing to the cost is the logistical problems encountered with theuse of organic type scavengers. In most embodiments, a transition metalcatalyst is used to activate an oxidizable polymer. A disadvantage ofthis technique is that the polymer begins reacting with oxygen as soonas the package is made. Consequently, the bottles must be filledimmediately. Higher amounts of scavenger are used to compensate for thescavenging capacity lost between the time the bottle is made and whenthe bottle is filled.

In another technique, UV radiation is used to activate the oxidizablepolymer. However, UV activation techniques are relatively expensive, andthe initiators are often not regulated for use in food packaging.Packages designed for beers and juices are specifically designed toprevent UV penetration, hence UV activation would not be practical forthese containers which block UV.

An alternative to a visually acceptable organic material is to usediscrete scavenging particles in the container sidewall, such as reducedmetal powders. Reduced iron powder is commonly used for oxygenscavenging in food packages. Iron reacts with the oxygen and forms ironoxide. Most applications also utilize a salt and a moisture absorber asreaction-enhancing agents to increase the effectiveness of the ironpowder. Because the reaction usually requires water, the iron scavengingcomposition remains inactive until the package is filled and thereaction is activated by the water of the packaged contents whichmigrates into the polymer and contacts the scavenging composition.

The use of scavenging powders in clear packages has previously beenlimited by aesthetics, particularly haze and color. High loadings ofiron powder, on the order of 500-5000 parts per million, are typicallyrequired to obtain sufficient oxygen absorption. Conventional wisdom andprior art teaches the practitioner to use the highest amount ofscavenging surface area possible so that the efficiency and capacity isincreased and the amount of iron added is minimized. In practice, thismeans a large number of small particles. Unfortunately, previousattempts at preparing resin compositions comprising high levels of smallparticles of iron for use in clear packages have resulted in packageswith poor optical properties. This is particularly true when the resincomposition is stretched or oriented to any degree in forming the finalarticle, such as in polyester bottles. Typically, bottles prepared fromsuch resin compositions are translucent. Haze values for these bottlesare generally high, and clarity is lacking.

Thus, there remains a need for packaging materials having acceptablevisual aspects and comprising activatable oxygen scavenging resincompositions.

BRIEF SUMMARY OF THE INVENTION

In general the present invention provides a container comprising aneffective amount of oxygen-scavenging particles and having low haze.More specifically, the present invention includes a container having atleast one wall, wherein the wall comprises a populated area, and whereinthe populated area comprises a film-forming polymer; and a population ofparticles comprising an effective amount of oxygen-scavenging particles,wherein the number of particles of said population does not exceed aconcentration of about

-   -   (6×10⁷ particles÷T) per cubic centimeter of polymer wherein T is        the thickness of the populated area in mils; and wherein the        wall has a transmission Hunter haze of up to about 1 percent per        mil of the container wall.

The iron or other oxygen scavenger is present in an amount sufficient toeffectively scavenge oxygen and provide longer shelf life foroxygen-sensitive materials. The particle size of the particle populationis optimized to provide effective scavenging activity, while reducinghaze.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a container and a container wall.The wall includes a populated area comprising a film-forming polymer.Suitable thermoplastic polymers for use in the present invention includeany thermoplastic homopolymer or copolymer. Examples of thermoplasticpolymers include polyamides, such as nylon 6, nylon 66 and nylon 612,linear polyesters, such as polyethylene terephthalate, polybutyleneterephthalate, polytrimethylene terephthalate, and polyethylenenaphthalate, branched polyesters, polystyrenes, polycarbonate, polyvinylchloride, polyvinylidene dichloride, polyacrylamide, polyacrylonitrile,polyvinyl acetate, polyacrylic acid, polyvinyl methyl ether, ethylenevinyl acetate copolymer, ethylene methyl acrylate copolymer,polyethylene, polypropylene, ethylene-propylene copolymers,poly(1-hexene), poly(4-methyl-1-pentene), poly(1-butene),poly(3-methyl-1-butene), poly(3-phenyl-1-propene) andpoly(vinylcyclohexane). Preferably, the thermoplastic polymer used inthe present invention comprises a polyester polymer or copolymer.

It will be understood that a film-forming polymer is one that is capableof being made into a film or sheet. The present invention is not,however, limited to films and sheets. The container of the presentinvention also includes bottle walls, trays, container bases, or lids.The walls of containers such as blown bottles and thermoformed trays canbe considered films or sheets that have been formed into the shape ofthe container, and are therefore also within the scope of the invention.Bases and lids of containers are also considered walls of a container.

Polymers employed in the present invention can be prepared byconventional polymerization procedures well known in the art. Thepolyester polymers and copolymers may be prepared by melt phasepolymerization involving the reaction of a diol with a dicarboxylicacid, or its corresponding diester. Various copolymers resulting fromuse of multiple diols and diacids may also be used. Polymers containingrepeating units of only one chemical composition are homopolymers.Polymers with two or more chemically different repeat units in the samemacromolecule are termed copolymers. The diversity of the repeat unitsdepends on the number of different types of monomers present in theinitial polymerization reaction. In the case of polyesters, copolymersinclude reacting one or more diols with a diacid or multiple diacids,and are sometimes referred to as terpolymers.

Suitable dicarboxylic acids include those comprising from about 6 toabout 40 carbon atoms. Specific dicarboxylic acids include, but are notlimited to, terephthalic acid, isophthalic acid, naphthalene2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediaceticacid, diphenyl-4,4′-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid,succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid,and the like. Specific esters include, but are not limited to, phthalicesters and naphthalic diesters.

These acids or esters may be reacted with an aliphatic diol having fromabout 2 to about 10 carbon atoms, a cycloaliphatic diol having fromabout 7 to about 14 carbon atoms, an aromatic diol having from about 6to about 15 carbon atoms, or a glycol ether having from 4 to 10 carbonatoms. Suitable diols include, but are not limited to, 1,4-butenediol,trimethylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,diethylene glycol, resorcinol, and hydroquinone.

Polyfunctional comonomers can also be used, typically in amounts of fromabout 0.1 to about 3 mole percent. Suitable comonomers include, but arenot limited to, trimellitic anhydride, trimethylopropane, pyromelliticdianhydride (PMDA), and pentaerythritol. Polyester-forming polyacids orpolyols can also be used.

One preferred polyester is polyethylene terephthalate (PET) formed fromthe approximate 1:1 stoichiometric reaction of terephthalic acid, or itsester, with ethylene glycol. Another preferred polyester is polyethylenenaphthalate (PEN) formed from the approximate 1:1 to 1:1.6stoichiometric reaction of naphthalene dicarboxylic acid, or its ester,with ethylene glycol. Yet another preferred polyester is polybutyleneterephthalate (PBT). Copolymers of PET, copolymers of PEN, andcopolymers of PBT are also preferred. Specific co and terpolymers ofinterest are PET with combinations of isophthalic acid or its diester,2,6 naphthalic acid or its diester, and/or cyclohexane dimethanol.

The esterification or polycondensation reaction of the carboxylic acidor ester with glycol typically takes place in the presence of acatalyst. Suitable catalysts include, but are not limited to, antimonyoxide, antimony triacetate, antimony ethylene glycolate,organomagnesium, tin oxide, titanium alkoxides, dibutyl tin dilaurate,and germanium oxide. These catalysts may be used in combination withzinc, manganese, or magnesium acetates or benzoates. Catalystscomprising antimony are preferred.

Another preferred polyester is polytrimethylene terephthalate (PTF). Itcan be prepared by, for example, reacting 1,3-propanediol with at leastone aromatic diacid or alkyl ester thereof. Preferred diacids and alkylesters include terephthalic acid (TPA) or dimethyl terephthalate (DMT).Accordingly, the PTF preferably comprises at least about 80 mole percentof either TPA or DMT. Other diols which may be copolymerized in such apolyester include, for example, ethylene glycol, diethylene glycol,1,4-cyclohexane dimethanol, and 1,4-butanediol. Aromatic and aliphaticacids which may be used simultaneously to make a copolymer include, forexample, isophthalic acid and sebacic acid.

Preferred catalysts for preparing PTF include titanium and zirconiumcompounds. Suitable catalytic titanium compounds include, but are notlimited to, titanium alkylates and their derivatives, titanium complexsalts, titanium complexes with hydroxycarboxylic acids, titaniumdioxide-silicon dioxide-co-precipitates, and hydratedalkaline-containing titanium dioxide. Specific examples includetetra-(2-ethylhexyl)-titanate, tetrastearyl titanate,diisopropoxy-bis(acetyl-acetonato)-titanium,di-n-butoxy-bis(triethanolaminato)-titanium, tributylmonoacetyltitanate,triisopropyl monoacetyltitanate, tetrabenzoic acid titanate, alkalititanium oxalates and malonates, potassium hexafluorotitanate, andtitanium complexes with tartaric acid, citric acid or lactic acid.Preferred catalytic titanium compounds are titanium tetrabutylate andtitanium tetraisopropylate. The corresponding zirconium compounds mayalso be used.

The polymer of this invention may also contain small amounts ofphosphorous compounds, such as phosphates, and a catalyst such as acobalt compound, that tends to impart a blue hue.

The melt phase polymerization described above may be followed by acrystallization step, then a solid phase polymerization (SSP) step toachieve the intrinsic viscosity necessary for bottle manufacture. Thecrystallization and polymerization can be performed in a tumbler dryerreaction in a batch-type system. Alternatively, the crystallization andpolymerization can be accomplished in a continuous solid state processwhereby the polymer flows from one vessel to another after itspredetermined treatment in each vessel.

The crystallization conditions preferably include a temperature of fromabout 100 EC to about 150 EC. The solid phase polymerization conditionspreferably include a temperature of from about 200 EC to about 232 EC,and more preferably from about 215 EC to about 232 EC. The solid phasepolymerization may be carried out for a time sufficient to raise theintrinsic viscosity to the desired level, which will depend upon theapplication. For a typical bottle application, the preferred intrinsicviscosity is from about 0.65 to about 1.0 deciliter/gram, as determinedby ASTM D-4603-86 at 30° C. in a 60/40 by weight mixture of phenol andtetrachloroethane. The time required to reach this viscosity may rangefrom about 8 to about 21 hours.

In one embodiment of the invention, the film-forming polymer of thepresent invention may comprise recycled polyester or materials derivedfrom recycled polyester, such as polyester monomers, catalysts, andoligomers.

At least one wall of the container of the present invention comprises apopulated area. There are technologies that can localize a population ofparticles into one area of a container wall. For example, where thecontact surface of the film or wall is the surface adjacent to thepackaged material, the oxygen scavenger could advantageously belocalized in an area at the contact surface. Examples of thesetechnologies include, but are not limited to, lamination, coextrusion,coinjection, and the like. Examples of technologies capable oflocalizing the population are further discussed U.S. Pat. Nos.5,153,038, 6,413,600, 4,525,134, 4,439,493 and 4,436,778 which arehereby incorporated by reference in their entirety. It has now beendiscovered that high levels of particles can be incorporated into filmsor walls made by using these technologies. The localized area in whichthe population of particles is substantially located is referred toherein as the populated area.

The populated area comprises a population of particles. The thickness ofthe populated area is measured cross-sectionally through the containerwall measuring from the contents side of the package wall to the outeredge of the wall and starts at the first particle of the population andends when 95% of the population has been accounted for. The thickness ofthe populated area in a monolayer film or container is the thickness offilm or container wall. In a container wall that is not a monolayer, thethickness of the populated area will be somewhat less than the thicknessof the wall. The thickness of the populated area of a laminated wall isthe thickness of the layer of the wall containing at least 95 percent ofthe population of particles. In multilayer films or walls wherein thelayers blend at the interface, such as those formed by coextrusion, thethickness of the populated area is the cross-sectional thickness oflayer containing at least about 95 percent of the population ofparticles.

In the case of two or more distinct populated areas, the thickness ofthe populated area is reduced by the thickness of the unpopulated areaor unpopulated areas lying between the inner and outermost populatedareas. This would be the case of an A−B−A structure where A containedthe population. The thickness of the populated area is the thickness ofA+B+A−B. in the case of A−B−A−B, the thickness is still A+B+A−B. Usingthe same principles, B−A−B−A−B has a thickness of A+B+A−B. A-B-A-B-A hasa population thickness of 3 xA-2 xB.

Preferably, the number of particles in the populated area does notexceed a concentration of about (6×10⁷ particles÷T) per cubic centimeterof polymer, wherein T is the thickness of the populated area in mils.More preferably, the number of particles in the populated area does notexceed a concentration of about (3×10⁷ particles÷T) per cubic centimeterof polymer, wherein T is the thickness of the populated area in mils.Even more preferably, the number of particles in the populated area doesnot exceed a concentration of about (1.5×10⁷ particles÷T) per cubiccentimeter of polymer, wherein T is the thickness of the populated areain mils.

The population of particles comprises oxygen-scavenging particles, aswell as any other components of the container, such as those discussedherein, that are present in the form of discrete particles.

Suitable oxygen-scavenging particles comprise at least one materialcapable of reacting with molecular oxygen. Desirably, materials areselected that do not react with oxygen so quickly that handling of thematerials is impracticable. Therefore, stable oxygen-scavengingmaterials that do not readily explode or burn upon contact withmolecular oxygen are preferred. From a standpoint of food safety,materials of low toxicity are preferred, however with properprecautions, this is not a limitation. The particles should notadversely affect the organoleptic properties of the final product.Preferably, the oxygen-scavenging particles comprise anoxygen-scavenging element selected from calcium, magnesium, scandium,titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper,zinc, silver, tin, aluminum, antimony, germanium, silicon, lead,cadmium, rhodium, and combinations thereof. More preferably, theoxygen-scavenging particles comprise an oxygen-scavenging elementselected from calcium, magnesium, titanium, vanadium, manganese, iron,cobalt, nickel, copper, zinc, or tin. Even more preferably, theoxygen-scavenging particles comprise iron. It will be understood thatthese oxygen-scavenging elements may be present as mixtures, incompounds such as oxides and salts, or otherwise combined with otherelements, with the proviso that the oxygen-scavenging elements arecapable of reacting with molecular oxygen. Metal alloys comprising atleast one oxygen-scavenging element are also suitable. Theoxygen-scavenging particles may contain impurities that do not affectthe practice of the present invention.

It is known in the art that certain substances enhance the oxygenscavenging reaction. In a preferred embodiment of the present invention,the oxygen-scavenging particles are pre-treated with one or morereaction-enhancing agents that facilitate the oxygen scavengingreaction. Any of the reaction-enhancing agents known in the art may beused.

In one embodiment of the present invention, the oxygen-scavengingparticles comprise iron. The iron reacts with oxygen in its function asan oxygen scavenger. Metallic iron, or alloys or mixtures containingmetallic iron may be used. Furthermore, it is to be understood that themetallic iron may contain impurities that do not affect the practice ofthe present invention.

At least three types of metallic iron powders are available:electrolytic, sponge, and carbonyl iron. Electrolytic iron is made viathe electrolysis of iron oxide, and is available in annealed andunannealed form from, for example, OM Group, Inc. Sponge iron isavailable from, for example, North American Höganäs, Inc. There are atleast two types of sponge iron: hydrogen-reduced sponge iron carbonmonoxide-reduced sponge iron. Carbonyl iron powder is available from,for example, Reade Advanced Materials. It is manufactured using acarbonyl decomposition process.

Depending upon the type of iron selected, the particles may vary widelyin purity, surface area, and particle shape. The following non-limitingexamples of typical characteristics are included herein to exemplify thevariation that may be encountered. Electrolytic iron is known for itshigh purity and high surface area. The particles are dendritic. Carbonyliron particles are substantially uniform spheres, and may have a purityof up to about 99.5 percent. Carbon monoxide-reduced sponge irontypically has a surface area of about 95 square meters per kilogram(m²/kg), while hydrogen-reduced sponge iron typically has a surface areaof about 200 m²/kg. Sponge iron may contain small amounts of otherelements, for example, carbon, sulfur, phosphorus, silicon, magnesium,aluminum, titanium, vanadium, manganese, calcium, zinc, nickel, cobalt,chromium, and copper.

The oxygen-scavenging particles are present in an effective amount foradequate oxygen-scavenging ability. If too few oxygen-scavengingparticles are present, too much oxygen may be able to pass through thecontainer wall without being scavenged. The amount required for adequateoxygen-scavenging ability depends on such factors as the application,the type of polymer used, the amount of gas barrier protection desired,the type of oxygen-scavenging particles, the particle size of theoxygen-scavenging particles, and moisture content of the packagedmaterial. Preferably, the oxygen-scavenging container of the presentinvention comprises at least about 50 parts oxygen-scavenging particlesper million parts by weight resin. More preferably, the container of thepresent invention comprises at least about 100 parts oxygen-scavengingparticles per million parts by weight resin. Even more preferably, thecontainer of the present invention comprises at least about 500 partsoxygen-scavenging particles per million parts by weight resin. Yet evenmore preferably, the container of the present invention comprises atleast about 1000 parts oxygen-scavenging particles per million parts byweight resin.

It has been found that containers such as film or bottle articlescomprising up to about 12,000 parts oxygen-scavenging particles permillion parts by weight resin (1.2 weight percent) can have acceptablehaze characteristics. For applications where haze is not an issue ofconcern, it will be appreciated that the amount of oxygen-scavenging orother particles may be much higher. Further characterization of thepopulation of particles that is necessary for practice of the presentinvention is provided hereinbelow.

The composition of the present invention may optionally further compriseone or more reaction-enhancing agents known in the art to facilitate theoxygen-scavenging reaction. Examples of known reaction-enhancing agentsare discussed in U.S. Pat. Nos. 5,744,056 and 5,885,481, herebyincorporated by reference in their entirety. Suitable agents arevariously described as hydroscopic materials, electrolytic acidifyingagents, non-electrolytic acidifying agents, metal halides, metalsulfates, metal bisulfates, and salts. The reaction-enhancing agents maybe added to the polymer melt, or during extrusion.

The composition of the present invention may optionally yet furthercomprise one or more components selected from the group consisting ofimpact modifiers, surface lubricants, denesting agents, stabilizers,crystallization aids, antioxidants, ultraviolet light absorbing agents,catalyst deactivators, colorants, nucleating agents, acetaldehydereducing agents, reheat reducing agents, fillers, branching agents,blowing agents, accelerants, and the like.

It will be understood that if the above-mentioned optional componentsmaintain their discrete nature within the resin, then they are part ofthe population of particles as defined herein.

High levels of particles can be incorporated into a polyester resincomposition with low haze. The particles may be admixed with thethermoplastic polymer during or after polymerization, with the polymermelt or with the molding powder or pellets from which the injectionmolded articles are formed, or from which the film or sheet is cast.Accordingly, the particles may be added during any of the process steps,such as during melt phase polymerization, after the melt phasepolymerization (post polymerization) but before pelletization, duringsolid state polymerization, and during extrusion. Alternatively, amasterbatch of oxygen-scavenging resin may be prepared, and then mixedor blended with additional resin. Preferably, the masterbatch contains arelatively high amount of particles, and the desired particleconcentration in the product polymer is achieved by mixing or blendingthe masterbatch with an amount of additional resin.

The container of the present invention advantageously possesses botheffective oxygen-scavenging functionality and acceptable opticalproperties. The optical properties of polymers are related to both thedegree of crystallinity and the actual polymer structure. Transparencyis defined as the state permitting perception of objects through asample. Transmission is the light transmitted. Transparency is measuredas the amount of undeviated light. In other words, transparency is theoriginal intensity of the incident radiation minus all light absorbed,scattered, or lost through any other means.

Many polymers are transparent, but polymers that are transparent tovisible light may become opaque as the result of the presence ofadditives such as fillers, stabilizers, flame retardants, moisture, andgases. The opacity results from light-scattering processes occurringwithin the material. The light scattering reduces the contrast betweenlight, dark, and other colored parts of objects viewed through thematerial and produces a milkiness or haze in the transmitted image. Hazeis a measure of the amount of light deviating from the direction oftransmittancy of the light by at least 2.5 degrees.

The color and brightness of a polyester article can be observedvisually, and can also be quantitatively determined by a HunterLab ColorQuest Spectrometer. This instrument uses the 1976 CIE a*, b*, and L*designations of color and brightness. An a* coordinate defines a coloraxis wherein plus values are toward the red end of the color spectrumand minus values are toward the green end. The b* coordinate defines asecond color axis, wherein plus values are toward the yellow end of thespectrum and minus values are toward the blue end. Higher L* valuesindicate enhanced brightness of the material.

Generally, the acceptable haziness of an article, such as a bottle orfilm, is determined visually. However, a HunterLab Color QuestSpectrometer can quantitatively indicate the haze of an article orresin. This quantitative measurement is referred to herein astransmission Hunter haze.

It is known in the art that a stretched film will often have more hazethan its unstretched counterpart. Therefore, haze measurements wereobtained on stretched and unstretched container walls and through thebottle itself

The container wall of the present invention may comprise unstretchedfilms or sheets. The manufacture of films and sheets is known in theart, and any one of a number of suitable techniques can be used toprepare the film.

The container of the present invention may also comprise bottlesexpanded from preforms. A preform is a formed structure that is expandedin a mold to form a bottle. Alternately, the container may comprisefilm, pouches, or other packaging material.

In general, polyester bottles are prepared in blow-molding processescarried out by heating the preform above the polyester glass transitiontemperature, placing the heated preform into a mold of the desiredbottle form, injecting air into the preform to force the preform intothe shape of the mold, and ejecting the molded bottle from the mold ontoa conveyor belt.

Two factors that must be taken into account when accurately measuringhaze of stretched material and comparing haze values are the thicknessof the article being measured, and the blow window.

In order to establish the proper temperature and processing time toobtain the lowest haze value due only to the crystallization process ofthe polyester resin, a blow window graph is constructed. The blow windowgraph shows haze as a function of the heat exposure time of the preform.The graph is usually constructed by creating isotherms and heating eachpreform at the same temperature for different lengths of time. Theheated preform is then stretched and the haze measurement is performedon the stretched portion. Several different temperatures are chosen.Generally, a resin will have a best temperature that produces the lowesthaze value, and that temperature is used to conduct the remainingevaluations. In the work described herein, one temperature was chosenand the parameter of time was varied to determine the optimum blowwindow.

While polyester has excellent optical properties, even when crystallizedthrough strain hardening (stretching), particulate additives can reducethe transparency and increase the haze. The number of particles and thesize of the particles affect the haze of both stretched and unstretchedfilms and articles. It will be appreciated by those skilled in the artthat the thermoplastic resins disclosed herein vary significantly indensity. Additionally, particles of the population may vary in density.Therefore, the preferred concentration of the population of particlesand scavenging particles within the resin is expressed as the number ofparticles per volume of the resin.

It will be understood that, within any particle population, theparticles are not all the same size, but comprise a range of particlesizes. Furthermore, the particles within the population may or may nothave a uniform, regular shape. The particle population, or any portionof the population, may be described by an average particle size, asmeasured by any of the standard techniques known in the art. Thesetechniques include measuring the equilibrium velocities of particlessettling through a liquid under the influence of gravity, resistancepulse counters, light blockage counters, image analyzers, laserdiffraction spectroscopy, and photon correlation spectroscopy.Statistical values commonly used to describe the particle size of aparticle population include: (1) geometric mean size, which is theaverage particle size calculated on a log basis; (2) arithmetic mean,which is the average particle size calculated on a linear basis; (3)median size, which is the 50^(th) percentile of the distribution; and(4) mode size, which is the most prevalent particle size of thedistribution. Further, the sample may be described by a particle sizerange, or as less than or equal to a given particle size. Thesedesignations may be determined by sieving techniques, or othertechniques known in the art. Thus, any given population of particleswill have a particle size distribution, which is a description of therange of particle sizes and the amounts of particles of each size.Techniques for particle size determination are further discussed by PaulWebb and Clyde Orr in Analytical Methods in Fine Particle Technology,Micromeritics Instrument Corp. (1997), and by James P. M. Syvitski inPrinciples, Methods, and Applications of Particle Size Analysis,Cambridge University Press (1991), both of which are hereby incorporatedby reference in their entireties.

Various parameters have been found to be desirable for the size ofparticles within the particle population. For example, it will beappreciated that particles larger than the thickness of the containerwall may produce a rough surface, so that significant amounts of suchlarge particles are to be avoided. In general, it is preferred that thesize of the particles fall within the range of from about 1 to about 70microns, more preferably from about 10 to about 70 microns, and evenmore preferably from about 15 to about 70 microns. Even yet morepreferably, that the size of the particles fall within the range of fromabout 20 to about 70 microns. It will be understood that these preferredranges are given as general guidelines only, and that a small number ofparticles may fall outside these ranges without affecting the essentialcharacteristics of the resin, and are therefore within the scope of thepresent invention.

Recitations throughout the specification and claims of “do not exceedabout 6.0×10⁷” are intended to include smaller amounts of particles,depending upon the amount that is preferred. Desirably, large amounts ofparticles are added to the resin and the impact on haze is minimized.This can be accomplished by selecting the particle size distribution ofthe population of particles, and controlling the total number ofparticles to keep it below a certain maximum value per unit volume ofpolymer. This maximum value is related to thickness of the populatedresin.

High levels of particles can be incorporated into a container wall withlow haze by a method comprising the steps of: providing a population ofparticles; selecting the particle size distribution of the population tocomprise an appropriate number of particles within the preferred sizerange; adding the population of particles to a polymer to form a mixtureof polymer and particles during one or more of the process steps of:melt phase polymerization of the polymer; post polymerization and priorto pelletization; solid state polymerization of the polymer; andextrusion; and forming a container having at least one wall by using themixture of polymer and particles.

As discussed above, the population of particles may be localized intoone or more populated areas of a container wall, by varioustechnologies. In this embodiment, the populated area comprises themixture of polymer and particles, and the method further comprises thestep of combining the mixture with additional polymer to form a wallhaving a populated area and at least one other area. The additionalpolymer may be a different polymer or the same polymer but without anyscavenger present.

The container, according to the present invention, can compriseunstretched films or sheet of any thickness typically employed in theart of polymer films.

In a preferred embodiment, the film has a thickness of at least about0.5 mils, and a transmission Hunter haze number of, preferably, lessthan about 10 percent, more preferably less than about 8 percent, andeven more preferably less than about 5 percent. While higher than thehaze numbers for polyester samples comprising no oxygen-scavenging orother particles, these haze values are well within the range of valuesacceptable for many commercial applications.

The container can comprise bottles wherein each bottle sidewall has athickness of from about 9 to about 35 mils, preferably from about 11 toabout 25 mils, and more preferably from about 14 to about 21 mils.

In a preferred embodiment, each bottle sidewall has a thickness of fromabout 14 to about 21 mils, and the bottle has a Hunter haze number of,preferably, less than about 10 percent, more preferably less than about8 percent, and even more preferably less than about 5 percent, atoptimum blow window conditions. While higher than the haze numbers forpolyester samples comprising no iron or other particles ofoxygen-scavenging composition, these haze values are well within therange of values acceptable for many commercial applications.

The maximum preferred concentrations of particles recited above weredetermined for unstretched films having a crystallinity of less thanabout one percent. In general, as the crystallinity of the polymer resinincreases, haze increases. It will therefore be understood that themaximum preferred concentration of particles will be lower in polymercompositions having higher crystallinity

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theGeneral Experimentation Section disclosed herein below. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

GENERAL EXPERIMENTATION Preparation of Examples Nos. 1-26

A PET copolymer resin was prepared by the teachings of U.S. Pat. No.5,612,423 that is incorporated herein by reference. Samples of ironparticles having various particle sizes were obtained. Hydrogen-reducedspong iron from Pyron was used for examples 1-10. Carbonyl iron powderobtained from ISP Technologies was used for examples 11-26. Thus, theiron particles used in Example No. 3 had a particle size range of about25 to about 38 microns. It will be understood that such a sample can beprepared, for example, by using sieves. The iron particles were added topolyester resin, by using a metered feeder on a twin-screw extruder, toform a masterbatch of resin containing 2.5 percent by weightiron-containing resin composition. This masterbatch was blended with thebase resin to obtain the desired concentration. The base resin/ironmixtures were dried under vacuum at 325 EF (163 EC) for 18 hours. Thedried resins were transferred to a Novotec drying hopper of a Nissei ASB50T Injection Blow-Molding machine. The hopper was heated to 325 EF (163EC) and set for a dew point of −40 EF (−40 E C).

The bottle preforms were manufactured and blown into bottles in atwo-step process. First, the preforms were prepared on a Mini-jector orNissei machine. Then, the bottles were blown from their preforms on aCincinnati Milacron Reheat Blow Lab (RHB-L) blow molding machine. Thepreforms were prepared on the Mini-jector using a cycle time of 45second, inject time of 15 seconds, with a rear heater temperature of 270EC, a front heater temperature of 275 EC, and a nozzle heat of 275 EC.The inject pressure was between about 1000 and about 1500 psig. The oventemperature on the Milacron RHB-L was from about 163 to about 177 EC.The exposure time was from about 31 to about 52 seconds.

The haze measurements were taken through the bottle sidewall, which isthe thinned, stretched portion. Because these measurements were taken onthe whole bottle, the thickness actually contains two sidewalls. AHunterLab Color QUEST Sphere Spectrophotometer System equipped with anIBM PS/2 Model 50Z computer, IBM Proprinter II dot matrix printer,assorted specimen holders, and green, gray and white calibration tiles,and light trap was used. The HunterLab Spectrocolorimeter integratingsphere sensor is a color and appearance measurement instrument. Lightfrom the lamp is diffused by the integrating sphere and passed eitherthrough (transmitted) or reflected (reflectance) off an object to alens. The lens collects the light and directs it to a diffractiongrating that disperses it into its component wave lengths. The dispersedlight is reflected onto a silicon diode array. Signals from the diodespass through an amplifier to a converter and are manipulated to producethe data. Haze data is provided by the software. It is the calculatedratio of the diffuse light transmittance to the total lighttransmittance multiplied by 100 to yield a “Haze %” (0% being atransparent material, and 100% being an opaque material). Samplesprepared for either transmittance or reflectance must be clean and freeof any surface scratches or abrasions. The size of the sample must beconsistent with the geometry of the sphere opening and in the case oftransmittance, the sample size is limited by the compartment dimension.Each sample is tested in four different places, for example on thebottle sidewall or representative film area.

A Panametrics Magna-Mike 8000 Hall Effect Thickness Gauge was employedto measure the bottle sidewall thickness. A small steel ball is placedon one side of the test material and a magnetic probe underneath. Thedistance between the ball and the probe is measured by means of the Halleffect sensor. More specifically, a Magna-Mike 8000 equipped with aDPU-411 thermal printer (type II), a remote foot switch, a target ballkit, and a Standard 801PR Probe was used. Two measurements were takenand averaged.

The iron particle concentration, average iron particle size, and thehaze values at a constant sample thickness of from about 11 to about 13mils and optimum blow window conditions are summarized in Tables 1 and2. Comparative Example Nos. 1, 6, and 11 contained no iron particles.The particle size of the iron particles reported in Table 1 was providedby the supplier. The particle size of the iron particles in Table 2 weredetermined as the geometric mean based upon volume. TABLE 1 IronParticles in Stretched Polyester Film Compositions Optimum Fe conc.Particle size reheat time Example No. (ppm) (microns) (sec) Haze (%) 1 0— 43 1.5 2 1250 # 25 49 7.56 3 1250 25-38 49 4.53 4 1250 38-45 52 4.58 51250 45-75 52 4.41 6 0 — 43 1.5 7 2500 # 25 46 14.08 8 2500 25-38 469.13 9 2500 38-45 46 8.45 10 2500 45-75 40 8.56

TABLE 2 Iron Particles in Stretched Polyester Film Compositions and HazeValues No. of particles Fe Particle per cm³ Optimum Example conc. sizepolymer reheat No. (ppm) (microns) (×10⁶) time (sec) Haze (%) L* 11 0 —0 43 1.5 90.89 12 100 3.23 0.3729 46 5.1 89.78 13 250 3.23 0.9324 406.98 88.66 14 500 3.23 1.8647 46 9.12 86.17 15 800 3.23 2.9836 46 11.6383.99 16 1000 3.23 3.7295 46 16.44 78.1 17 100 4.787 0.0750 49 4.5589.76 18 250 4.787 0.1875 49 6.74 89.73 19 500 4.787 0.3750 46 9.0488.27 20 800 4.787 0.5999 46 11.8 87.21 21 1000 4.787 0.7499 46 12.9983.68 22 100 7.819 0.0483 49 5.4 90.51 23 250 7.819 0.1207 46 6.85 89.8324 500 7.819 0.2415 43 8.49 88.79 25 800 7.819 0.3864 49 7.83 88.06 261000 7.819 0.4830 46 8.81 87.27

Preparation of Examples Nos. 27-32

Examples 27 through 32 are also stretched film samples prepared asabove. Results are shown in Table 3. The type of iron used for Examples27-29 was unannealed electrolytic iron having a geometric mean particlesize based upon volume of about 10.84 microns. The iron used forExamples 30-32 was carbon monoxide-reduced sponge iron having ageometric mean particle size based upon volume of about 18.61 microns.While the parts iron by weight per million parts by weight polymer arecomparable, the number of particles per cubic centimeter polymerincrease with decreasing particle size, and the transmission Hunter hazeper mil thickness of the film also increases. It should be noted thatfor examples 27-32, the haze measurement was taken on the bottlesidewall only and was not taken through the complete bottle. TABLE 3Variation of Particle Size, Number of Particles, and Haze No. ofParticles per Example PPM Iron cc³ Polymer Thickness Haze per mil No.(by weight) (× 10⁶) (mils) (%) 27 1000 0.2183 13.0 0.257 28 2000 0.436511.0 0.532 29 3000 0.6548 13.0 0.630 30 1000 0.0296 11.0 0.094 31 20000.0593 11.0 0.155 32 3000 0.0889 11.0 0.254

Preparation of Examples Nos. 33-44

In order to investigate the optimum concentration of particles ofvarious sizes in unstretched resin, films were made by using a Haakemixer. 2500.0 grams of HiPERTUF 89010 copolyester resin was weighed intoeach of several 1-gallon cans and dried in a vacuum oven under fullvacuum at about 100° C. overnight. The vacuum was restored toatmospheric pressure with nitrogen. Appropriate amounts of carbonyl-typeiron powder, manufactured by ISP Technologies was weighed under nitrogeninto vials for the different concentrations desired. The nominalparticle size range of the iron provided by the supplier was about 7 toabout 9 microns. The geometric mean particle size based on volume forthis iron powder was about 7.819 microns. The iron was added to theresin just prior to removing the hot resin from the oven, the vials weresealed, and the mixture was blended on a roller mill for about 5minutes.

The blended mixture was added to the feed hopper of a Haake Polylabextrusion system for film production. The resin was melted in theextruder and forced out of the die in the form of a flat sheet. Thethin, unoriented, substantially amorphous film was fed through a 3-rolltemperature-controlled polishing stack, quenched to minimizecrystallinity and to give a final, polished surface. The cooled film waswound onto a core. The thickness of the films measured in mils, thepercent transmission Hunter haze, and the percent haze per mil fortypical film samples having a constant concentration of iron are shownin Table 4. The concentration of iron is about 0.9659×10⁶ particles percubic centimeter polymer for Examples 33 and 34, and about 2.8978×10⁶particles per cubic centimeter polymer for Examples 35-37. It can beseen that, while haze increases with increasing film thickness, the hazeper mil of film thickness stays constant.

In Examples 38-44, the thickness of the films was kept constant at about11 mils, number of particles per cubic centimeter of polymer was varied.It can be seen that the haze per mil thickness increases with increasingparticle concentration. TABLE 4 Dependency of Haze on Thickness ofPopulated Area (T) Thickness Example No. Fe Conc (ppm) T (mils) Haze (%)Haze/mil 33 2000 11 2.17 0.197 34 2000 15 3.07 0.205 6000 35 6000 115.29 0.481 36 6000 15.3 6.68 0.437 37 6000 20 8.78 0.439

TABLE 5 Dependency of Haze on Number of Particles No. of Particles percm³ Polymer Thickness T Example No. Fe Conc (ppm) (× 10⁶) (mils)Haze/mil 38 0 0 10 0.035 39 1000 0.483 11 0.127 40 2000 0.9659 11 0.19741 3000 1.4489 11 0.302 42 6000 2.8978 11 0.481 43 10000 4.8297 11 0.74544 12000 5.7956 10.7 0.880

Haze values of less than 10% are obtained, even at iron levels of 2500ppm, when the iron particle size is greater than about 25 microns, asshown in Table 1. At 1250 ppm iron, and also at 2500 ppm iron, thehighest haze values were obtained when the average particle size wasless than or equal to about 25 microns, i.e., Example Nos. 2 and 7,respectively. Nevertheless, when the iron particle size is less than orequal to about 25 microns, haze values of less than 10% are obtained atiron levels up to about 1250 ppm. As shown in Table 2, when the ironparticle size is less than or equal to about 8 microns, haze values ofless than 10% are obtained at iron levels up to about 800 ppm.Furthermore, when the iron particle size is less than or equal to about5 microns, haze values of less than 10% are obtained at iron levels upto about 500 ppm.

When the population of particles is a constant parts by weight permillion parts polymer, the number of particles per cubic centimeter ofpolymer decreases as the particle size increases, as shown in Table 3.The overall transmission Hunter haze increases as the thickness of thesample increases, as shown in Table 4, however the haze per mil ofthickness stays relatively constant. Haze values of less than 1.0% permi of a container wall are obtained at concentrations of particles of upto (6×10⁷ particles÷T) per cubic centimeter of polymer, wherein T is thethickness of the populated area in mils, as shown in Table 5.

As should now be understood, the present invention overcomes theproblems associated with the prior art by providing a thermoplasticresin composition which contains an effective amount ofoxygen-scavenging particles and which has acceptable color and hazecharacteristics. The resulting resin can be used to form transparentbottles, films, and other containers and packaging materials. Thesematerials comprise oxygen-scavenging particles in an amount sufficientto effectively scavenge oxygen and provide longer shelf life foroxygen-sensitive materials. Furthermore, these materials have acceptablehaze characteristics.

While the best mode and preferred embodiment of the invention have beenset forth in accordance with the Patent Statutes, the scope of thisinvention is not limited thereto, but rather is defined by the attachedclaims. Thus, the scope of the invention includes all modifications andvariations that may fall within the scope of the claims.

1. A container having at least one wall, wherein the wall comprises apopulated area, and wherein the populated area comprises: a film-formingpolymer selected from the group consisting of polyethyleneterephthalate, copolymers of polyethylene terephthalate, polyethylenenaphthalate, copolymers of polyethylene naphthalate, polybutyleneterephthalate, copolymers of polybutylene terephthalate,polytrimethylene terephthalate, and copolymers of polytrimethyleneterephthalate; and a population of particles comprising an effectiveamount of oxygen-scavenging particles, wherein the number of particlesof said population does not exceed a concentration of about (6×10⁷particles÷T) per cubic centimeter of polymer wherein T is the thicknessof the populated area in mils; wherein the oxygen scavenging particlescomprise an element selected from the group consisting of calcium,magnesium, scandium, titanium, vanadium, chromium, manganese, iron,cobalt, nickel, copper, zinc, silver, tin, aluminum, germanium, silicon,lead, cadmium, and rhodium; wherein said wall has a transmission Hunterhaze of up to about 1 percent per mil of the container wall; and saidwall is of a multilayer construction.
 2. The container of claim 1,wherein the film-forming polymer is selected from the group consistingof copolymers of polyethylene terephthalate, copolymers of polyethylenenaphthalate, copolymers of polybutylene terephthalate, and copolymers ofpolytrimethylene terephthalate and the film forming polymer is preparedfrom one or more polyfunctional comonomers.
 3. The container of claim 2,wherein said polyfunctional comonomers are selected from the groupconsisting of pyromellitic dianhydride and pentaerythritol.
 4. Thecontainer of claim 1, wherein said oxygen-scavenging particles compriseiron.
 5. The container of claim 2, wherein said oxygen-scavengingparticles comprise iron.
 6. The container of claim 3, wherein saidoxygen-scavenging particles comprise iron.
 7. The container of claim 1,wherein said oxygen-scavenging particles comprise iron, and wherein saidoxygen-scavenging particles are present in an amount of from about 50 toabout 12,000 parts per million by weight of the resin.
 8. The containerof claim 1, wherein said population of particles further comprisesreaction-enhancing particles.
 9. The container of claim 8, wherein saidreaction-enhancing particles comprise hydroscopic materials,electrolytic acidifying agents, non-electrolytic acidifying agents,metal halides, metal sulfates, metal bisulfates, or mixtures thereof.10. The container of claim 1, wherein said oxygen-scavenging particlesare pretreated with at least one reaction-enhancing agent.
 11. Thecontainer of claim 1, wherein said container is a stretched bottlehaving a sidewall thickness of from about 11 to about 25 mils and aHunter haze value of about 10% or less.
 12. The container of claim 7,wherein said container is a stretched bottle having a sidewall thicknessof from about 11 to about 25 mils and a Hunter haze value of about 10%or less.
 13. The container of claim 10, wherein said container is astretched bottle having a sidewall thickness of from about 11 to about25 mils and a Hunter haze value of about 10% or less.